Technical Field of the Invention
The invention concerns a wing profile sail wherein a sailcloth defines an airfoil-shaped space which can be filled with air through openings equipped within one-way closing mechanisms.
Over the years a number of different types of wing profile sails have been developed in the field of sails for sailing boats, where attempts have been made to give the sail surfaces the most aerodynamically favourable shape in order to achieve maximum utilisation of the wind forces. A variety of models have been developed from profiled masts in which the actual sail forms an extension of the mast profile, to sails where the sailcloth defines spaces, which may have the aerodynamic shape of airfoils. Examples of these can be found, e.g., in British patent publication 2196310 and U.S. Pat. Ser. No. 4,753,186. In the British publication stays are used for forming the sail's outer surfaces in the most favourable way possible and for changing the sail's profile according to wind direction, while in the U.S. publication an inflatable lung or bag is place inside the sail for adapting its profile to wind influence.
The effect which is achieved with such "three-dimensional" sails is that the wind which strikes the wing profile sail on the windward side on the bow will have a longer flow path on the sail's convex side than on the sail's flat or slightly concave opposite side, thus generating a force component over the sail's convex side. The different air flow paths on the two sides of the sail will enable a vessel equipped with a wing profile sail of this kind to sail close to the wind to a far greater extent than a similar vessel with conventional sails.
In the applicant's previous Norwegian patent application 924572 a wing profile sail is described with two side sailcloths and an intermediate pocket or lung, which is filled with air via valve openings. In this design the sail's two side sailcloths are connected in front of and at the rear of the sail, with the result that the sail's inner space extends right out to the after leech. The sail is further shaped by the point in the front edge. Thus, in the same way as a traditional sail, the sail will have a narrow groove with great efficiency when the vessel is sailing closehauled for the greater deviation of angles of attack obtained against the wind will cause the wind to lose its force at the forward portion of the sail.
In the hitherto known wing profile sails no success has been achieved in obtaining an entirely favourable profiling, with the result that the above-mentioned driving force on the sail and thereby on the boat has not been as great or as efficient as desired. Thus it is an object of the invention to provide a wing profile sail which can supply the most optimal profiling possible.
A further problem with the known wing profile sails has been that they have not been entirely easy to handle, either during sailing or when hauling in and stowing away the sails.